In a molding operation, whether this be in an injection molding environment or any similar system using platens and molds, molded part quality and the overall efficiency/productivity of the molding machine is affected by a number of factors, including the physical conditions and configuration of the molding system equipment and also the processing conditions under which the molded part is formed. As a result, proper set-up a molding system may allow the molding system to operate at or near its peak efficiency.
One factor that affects the operation and efficiency of a molding system is setting of the process control parameters. The number and type of process control parameters depends on, at least in part, the configuration of the molding system equipment (for example, but not limited to, the number and type of sensors and the type and range of adjustments of the individual components of the molding system), the specifics of the article to be molded (including, but not limited to, the size and shape of the article and the resin(s) used to manufacture the article), the skill/experience of the operator, as well as the requirements of the end user/customer.
Examples of process control parameters include, but are not limited to, temperature, pressure, and flow rate profiles through the various components of the molding machine, mold and injection set-up. In this regard, it will be understood that the resin should be maintained within a range of acceptable temperature and pressure values or the resin may break-down and deteriorate or begin to solidify. Additionally, cavity filling is subject to numerous process transition points, particularly exemplified by the transition from velocity fill control (in which speed and position of a plunger in the shooting pot is critical) to pressure control (where preform shrinkage is addressed through the controlled injection of additional molten material). More particularly, the transition points are particularly important to preform geometry in heavier preforms where shrinkage is more significant, although it is noted that thin-walled and relatively lightweight preforms (less than about fifty grams) have particular fill control issues especially associated with the geometry and thickness transition between the elongate wall portion and the neck portion of the preform. Indeed, in the pressure hold portion of the cycle, there are usually multiple transitions to decreasing pressure for stipulated hold times for a particular preform geometry. The fill profile does, therefore, have an overall effect on cycle time.
Other process control parameters include, but are not limited to, resin density, the use of colorants or additives and whether the mold's venting system is operating to specification. As will be understood, colorants and additives are the choice of the customer and affect plastification and hence screw throughput capacity. With respect to venting, each cavity initially contains air that must be purged from the cavity during material injection. With a well-maintained and clean mold, higher fill rates are achieved because air vents from the cavity are initially clear from clogging particulate matter, for example PET dust and the like. With the partial or full blockage of the venting system, cavity pressures increase on a cavity-by-cavity basis and, in the extreme, non-purged air from cavities produces both voids in the molded article and short-weight molded products.
Process control parameters may further be affected by the component/set-up of the molding machine. For example, in the exemplary context of an injection molding machine, different components (such as, but not limited to, different plasticizing units with a different throughputs, processing speeds or screw diameters) may affect the set-up and optimization of the molding machine. Additionally, an injection molding machine may or may not include a nozzle mixer, or the nozzle mixer could be different between the test rig and the customer's machine. Furthermore, as regards the accumulation, prior to injection of a shot of plastic melt in a shooting pot (or in front of a reciprocating screw system), the volume of the shooting pot may vary. All of these differing configurations impact process control and optimization.
Also, in the injection molding field and particularly in relation to preform manufacture using PET molds, the customer may modify the mold to produce different components. In terms of stack components, such modification may simply require replacement of a cavity and gate insert, with a neck finish (defined by a neck ring) remaining unchanged. This form of mold conversion would therefore simply change the weight of the preform, since the geometry of the preform is changed by the variation of the length of the cavity or the thickness of the walls of the preform (as principally defined by the cavity). Again, such a change would require the injection molding machine set-up to be re-configured, which re-configuration requires time and expertise.
With any failure to appropriately set-up the process control parameters, the molded articles may include defects (either visually or structural defects), the molding machine may be damaged, and the overall efficiency and productivity of the molding machine may be decreased. Accordingly, it is generally desirable to optimize the process control parameters of the molding machine.
One known method of optimizing a molding machine relies heavily upon the skill, experience, and knowledge of the molding machine operator. In general, the molding machine operator may establish an initial set of process parameters based on the skill, experience, and knowledge of the molding machine operator. The molding machine operator may then monitor the molded part quality and adjust one or more of the process parameters in an effort to optimize the quality of the molded part as well as the overall productivity/efficiency of the molding machine. Unfortunately, the optimization process may take a considerable time even for a skilled molding machine technician.
Other methods and devices have been developed for controlling various aspects of the molding process equipment. For example, U.S. Patent Application No. 2004/0258787 describes in the abstract a control module that is attached to a machine platen of an injection molding machine. The control module is coupled to at least one sensor that reports a value of a processing condition associated with an injection mold and is disposed within the injection mold. The control module is also coupled to at least one controllable device that varies the processing condition of the injection mold and is disposed within the injection mold. The control module collects and processes sensor output, and provides a control signal to at least one controllable device. A display interface module is linked to the control module. The display interface module accepts user-entered data set-points, provides the user-entered data set-points to the control module, and collects the processed sensor output from the control module for display to a user.
It is important to note that the present disclosure is not intended to be limited to a system or method which must satisfy one or more of any stated or implied objects or features of the present disclosure. It is also important to note that the present disclosure is not limited to the preferred, exemplary, or primary embodiment(s) described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present disclosure, which is not to be limited except by the following claims.